The invention relates to golf balls and, more particularly, to golf balls having covers and intermediate layers which comprise a saturated polyurethane, and methods for making the same. Preferably, the cover of the golf ball is formed from a saturated polyurethane to produce a UV stable cover.
Golf ball covers are formed from a variety of materials, including balata and ionomer resins. Balata is a natural or synthetic trans-polyisoprene rubber. Balata covered balls are favored by the more highly skilled golfers because the softness of the cover allows the player to achieve spin rates sufficient to more precisely control ball direction and distance, particularly on shorter shots.
However, balata covered balls are easily damaged, and thus lack the durability required by the average golfer. Accordingly, alternative cover compositions have been developed in an attempt to provide balls with spin rates and a feel approaching those of balata covered balls, while also providing a golf ball with a higher durability and overall distance.
Ionomer resins have, to a large extent, replaced balata as a cover stock material. Chemically, ionomer resins are a copolymer of an olefin and an alpha, beta ethylenically-unsaturated carboxylic acid having 10-90% of the carboxylic acid groups neutralized by a metal ion. See U.S. Pat. No. 3,264,272. Commercially available ionomer resins include, for example, copolymers of ethylene and methacrylic or acrylic acid neutralized with metal salts. These are sold by E.I. DuPont de Nemours and Co. under the trademark SURLYN(copyright) and by the Exxon Corporation under the trademark ESCOR(copyright) and the trademark IOTEK(copyright). These ionomer resins are distinguished by the type of metal ion, the amount of acid, and the degree of neutralization.
U.S. Pat. Nos. 3,454,280, 3,819,768, 4,323,247, 4,526,375, 4,884,814, and 4,911,451 all relate to the use of SURLYN(copyright)-type compositions in golf ball covers. However, while SURLYN(copyright) covered golf balls as described in the preceding patents possess virtually cutproof covers, they have inferior spin and feel properties as compared to balata covered balls.
Polyurethanes have also been recognized as useful materials for golf ball covers since as early as about 1960. U.S. Pat. No. 3,147,324, filed Oct. 20, 1960, is directed to a method of making a golf ball having a polyurethane cover. The curing agents disclosed are diamines, polyols or air moisture. The disclosed polyurethane covered golf balls are durable, while at the same time maintaining the xe2x80x9cfeelxe2x80x9d of a balata ball.
Since 1960, various companies have investigated the usefulness of polyurethane as a golf ball cover material. U.S. Pat. No. 4,123,061 issued Oct. 31, 1978 teaches that a golf ball can be made from a polyurethane prepolymer of polyether and a curing agent, such as a trifunctional polyol, a tetrafunctional polyol or a diamine. U.S. Pat. No. 5,334,673 issued Aug. 2, 1994 discloses the use of two categories of polyurethane available on the market, i.e., thermoset and thermoplastic polyurethanes for forming golf ball covers, and in particular, thermoset polyurethane covered golf balls made from a composition of polyurethane prepolymer and a slow-reacting amine curing agent and/or a difunctional glycol.
The first commercially successful polyurethane covered golf ball was Titleist""s PROFESSIONAL golf ball in 1993. The principal reason for the delay in bringing polyurethane composition golf ball covers on the market was that it was a daunting engineering task to apply a covering of polyurethane composition to a golf ball core to form a golf ball cover having a uniform thickness.
In particular, the difficulty resided in centering a golf ball core in an amount of polyurethane that was sufficiently cured to keep the core centered while at the same time being insufficiently cured so that the cover material could be molded around the core. Resolution of this problem thus enabled production of the aforesaid PROFESSIONAL polyurethane covered golf ball to commence in 1993.
Unlike SURLYN(copyright) covered golf balls, polyurethane golf ball covers can be formulated to possess the soft xe2x80x9cfeelxe2x80x9d of balata covered golf balls. However, golf ball covers made from polyurethane have not, to date, fully matched SURLYN(copyright) golf balls with respect to resilience or the rebound of the golf ball cover, which is a function of the initial velocity of a golf ball after impact with a golf club.
Furthermore, because the polyurethanes used to make the covers of such golf balls contain an aromatic component, e.g., an aromatic diisocyanate, polyol or polyamine, they are susceptible to discoloration upon exposure to light, particularly UV light. To slow down the discoloration, light and UV stabilizers, e.g., Tinuvin 770, 765 and 328, are added to these aromatic polymeric materials. However, to further ensure that the covers formed from aromatic polyurethanes do not appear discolored, the covers are painted with white paint and then with a clear coat to maintain the white color of the golf ball. The application of a uniform white pigmented coat to the dimpled surface of the golf ball is a difficult process which adds time and costs to the manufacture of the golf ball. Thus, there remains a need for polyurethane materials which do not discolor and which are suitable for forming a golf ball.
The invention is directed to a golf ball having at least one layer, formed of a saturated polyurethane. The term xe2x80x9csaturatedxe2x80x9d as used herein refers to polyurethanes having saturated aliphatic and alicyclic polymer backbones, i.e., with no double bonds. In particular, the invention relates to a golf ball having at least one layer, such layer being formed of a saturated polyurethane, which is substantially free of unsaturated carbon-carbon bonds or aromatic groups. In this regard the components used in forming the saturated polyurethanes as used in the invention should be substantially free of unsaturated carbon-carbon bonds or aromatic groups. Thus, the saturated polyurethane should be formed of saturated polyols, saturated diisocyanates and saturated curing agents.
The use of such polyurethanes in the golf ball cover obviates the need to paint the golf ball with white paint prior to applying a clear topcoat to the ball. Unlike polyurethanes which contain aromatic groups or moieties, the saturated polyurethanes used in forming the golf balls of the present invention do not discolor upon exposure, especially repeated or extended exposure, to light. Also, by eliminating at least one coating step, the manufacturer realizes economic benefits in terms of reduced process times and consequent improved labor efficiency. Further, significant reduction in volatile organic compound (xe2x80x9cVOCxe2x80x9d) levels may be realized, as such VOC""s are a typical constituent of the paint used on golf balls. Therefore, the use of saturated polyurethanes to form white covered golf balls offers significant environmental, as well as cost, benefits.
If desired, although, as noted above, it is not necessary to paint the golf balls of the invention, the saturated polyurethanes used in forming the golf balls of the invention may be used in golf balls which are painted white. The value of such balls may be enhanced due to the enhanced color stability provided by the saturated polyurethanes as the surface paint is removed from the ball during the course of play. Such golf balls will not demonstrate the discoloration often observed in golf ball covers constructed of aromatic polyurethanes.
While saturated polyurethanes will generally be used in forming some or all of the cover of the golf ball of the invention, they may also or alternatively comprise one or more intermediate layer(s) located between the cover and the core. The saturated polyurethane may comprise anywhere from 1 to 100% by weight of the intermediate layer(s) and/or the cover of the golf ball.
A xe2x80x9ccoverxe2x80x9d or a xe2x80x9ccorexe2x80x9d as these terms are used herein includes a structure comprising either a single layer or one with two or more layers. As used herein, a core described as comprising a single layer means a unitary or xe2x80x9cone-piecexe2x80x9d core. The xe2x80x9clayerxe2x80x9d thus includes the entire core from the center of the core to its outer periphery. A core, whether formed from a single layer or from two or more layers may serve as a center for a wound ball. An intermediate layer may be incorporated, for example, with a single layer or multilayer cover, with a single layer or multilayer core, with both a single layer cover and core, or with both a multilayer cover and a multilayer core. A layer may additionally be composed of a tensioned elastomeric material, i.e., known as a wound layer. Intermediate layers of the type described above are sometimes referred to in the art, and, thus, herein as well, as an inner cover layer, as an outer core layer, or as a mantle layer.
The invention is directed in a first embodiment to one-piece golf balls comprised of a saturated polyurethane, as well as to other embodiments involving two-piece and multi-component, e.g., three-piece, golf balls comprising at least one cover layer and a core, wherein at least one cover layer comprises at least one saturated polyurethane, as well as multi-component golf balls comprising cores or covers having two or more layers, wherein at least one such layer(s) is formed of at least one saturated polyurethane.
More particularly, the present invention is directed, in a first embodiment, towards a golf ball comprising at least a cover and at least one core layer wherein the cover is formed from a composition comprising at least one saturated polyurethane.
The present invention is further directed in a second embodiment towards a golf ball comprising a cover, a core and at least one intermediate layer interposed between the cover and an outermost core layer, wherein the intermediate layer is formed from a composition comprising at least one saturated polyurethane.
The present invention is yet further directed in a third embodiment towards a golf ball comprising a cover, a core and at least one intermediate layer interposed between the cover and the core, wherein the outermost cover layer and at least one intermediate layer are both formed from a composition comprising at least one saturated polyurethane.
In the golf ball cover embodiment of the present invention, the saturated polyurethane preferably comprises from 1 to 100% by weight of the cover, with the remainder of the cover, if any, being comprised of one or more compatible, resilient polymers such as would be known to one of ordinary skill in the art.
Preferably, the saturated polyurethanes used in forming the golf balls of the present invention can be formed in accordance with the teachings described in U.S. Pat. No. 5,334,673, described above, and U.S. Pat. No. 5,484,870. U.S. Pat. No. 5,484,870 describes polyurea compositions, including golf balls employing covers formed of such polyurea compositions, comprising the reaction product of an organic isocyanate and an organic amine, each having at least two functional groups.